Recently, interest in energy storage technology has been increased. As application thereof spreads to the fields of cellular phones, camcorders, notebook PCs, and additionally, energy for electric vehicles, electrochemical devices have researched and developed. Electrochemical devices are most interesting field in such aspects, and development of secondary batteries capable of being charged and discharged has become the focus of attention. Recently, to improve capacitance density and specific energy of batteries, researches and developments for new electrodes and batteries have been performed.
Lithium secondary batteries developed early in 1990's among secondary batteries currently applied have a much higher operating voltage and energy density than typical batteries such as Ni-MH, Ni—Cd, and lead sulfate batteries. However, such lithium secondary batteries have limitations such as ignition and explosions caused by using organic electrolytes and complicated manufacturing processes.
Such secondary batteries are configured to have a structure in which an electrode assembly having a structure of a cathode/a separator/an anode, which is chargeable and dischargeable, is mounted on a battery case. As a general example of the electrode assembly, there are jelly-roll type electrode assemblies.
However, in the case of jelly-roll type electrode assemblies, during winding and compressing processes, due to a flat portion and a curve portion, breaks and cracks occur at the curve portion.